The present invention relates to an electrophotographic copying machine and, more particularly, to a copying process in an electrophotographic copying machine which includes a combined developing-cleaning magnetic brush unit.
An electrophotographic copying machine has been proposed, which has a combined developing-cleaning unit for selectively performing a developing operation and a cleaning operation. A typical system of the above-mentioned electrophotographic copying machine is described in U.S. Pat. No. 3,647,293 entitled "COPYING SYSTEM FEATURING COMBINED DEVELOPING-CLEANING STATION ALTERNATELY ACTIVATED" issued on Mar. 7, 1972. In this system, a magnetic brush element performs the developing operation at the first round of the photosensitive drum. At the second round of the photosensitive drum, a suitable bias voltage is applied to the magnetic brush element for cleaning the drum surface. The combined developing-cleaning magnetic brush element is effective to minimize the size of the electrophotographic copying machine. However, the copying speed is inevitably reduced because the photosensitive drum must rotate twice to complete one sheet copying operation.
Accordingly, an object of the present invention is to provide an improved copying process for an electrophotographic copying machine having a combined developing-cleaning magnetic brush element.
Another object of the present invention is to speed up the copying operation in an electrophotographic copying machine having a combined developing-cleaning magnetic brush element.
Still another object of the present invention is to provide a copying process in an electrophotographic copying machine, which ensures a uniform characteristic of a photosensitive drum surface.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a combined developing-cleaning magnetic brush element is disposed in an electrophotographic copying machine. A copy paper size detection element is provided for detecting a copy paper size and developing a first detection signal when, for example, the copy paper is greater than A.sub.4. If the copy paper is smaller than or equal to A.sub.4, the copy paper size detection element develops a second detection signal.
When the first detection signal is developed, the copying operation is conducted in the same manner as the conventional copying machine. That is, the photosensitive drum is rotated twice to complete one sheet of copying operation. When the second detection signal is developed, the copying machine of the present invention functions to divide the photosensitive drum surface into two regions. While the photosensitive drum rotates through the first revolution, the combined developing-cleaning magnetic brush element functions to develop a first region and to clean a second region. During the second revolution of the photosensitive drum, the first region is cleaned by the combined developing-cleaning magnetic brush element, and the second region is developed by the combined developing-cleaning magnetic brush element. That is, by dividing the photosensitive drum surface into two regions, the copying speed is enhanced when the copying machine is placed in the multi-copy mode and the copy paper is smaller than a half size of the surface of the photosensitive drum.